RT Journal Article SR Electronic T1 Millions of Boreal Shield Lakes can be used to Probe the Evolution of Archaean Ocean Life JF bioRxiv FD Cold Spring Harbor Laboratory SP 054478 DO 10.1101/054478 A1 SL Schiff A1 JM Tsuji A1 L Wu A1 JJ Venkiteswaran A1 L Molot A1 RJ Elgood A1 MJ Paterson A1 JD Neufeld YR 2016 UL http://biorxiv.org/content/early/2016/05/20/054478.abstract AB Ancient oceans on Earth were rich in iron, low in sulfur, and free of oxygen. The evolution of life, the onset of photosynthesis, and the subsequent oxidation of Earth's early oceans and atmosphere have long fostered intense debate. Very few analogous modern systems have been identified for study and most evidence has been gleaned from the sedimentary rock record, spurred by controversy surrounding the origin of the globally ubiquitous and extensive banded iron formations (BIFs). Here we provide the first evidence that Boreal Shield lakes can serve as modern analogues for the Archaean ocean. Specifically, we combine isotopic and molecular data to demonstrate that photoferrotrophy, a process involving photosynthetic fixation of carbon using reduced iron as an electron donor, occurs in the anoxic zone of stratified boreal lakes that are naturally low in sulfur and rich in iron. Further, anoxygenic photosynthetic processes are active in the water column, are prominent in the total metabolism of these bottom waters, and are marked by distinctive patterns in naturally occurring isotopes of carbon, nitrogen, and iron. Most importantly, these processes are robust, returning after water column re-oxygenation following lake turnover. Evidence of coupled iron oxidation, iron reduction, and methane oxidation has implications for both early Earth and modern systems. Previous studies have been confined to permanently stratified but low sulfur lakes on the assumption that photoferrotrophic bacteria are oxygen intolerant. Given that Boreal Shield lakes and ponds number in the tens of millions, and several can be manipulated experimentally, opportunities for exploring the evolution of life on ancient Earth are now greatly expanded.